1. Field of the Invention
The present invention relates to semiconductor device technology, more specifically to a structure of insulator film using a porous low dielectric constant film.
2. Description of the Related Art
Along with the miniaturization of semiconductor devices, transmission delays and signal interruption by crosstalk between wirings have become a subject to closer examination. Copper (Cu) having a lower resistivity than aluminum (Al) has been adopted as a metal wiring and a method for suppressing wiring resistance by 30% has been employed. A low-k film having a lower dielectric constant than a silicon oxide film (SiO2) has been adopted as an interlayer insulating film and a method of reducing capacitance between wirings has also been examined.
In order to provide an insulating film having a low dielectric constant, a porous low dielectric film (hereinafter called “porous-low-k film”) is achieved by providing microscopic pores in an insulating film and thus decreasing an apparent relative dielectric constant. Particularly, deposition methods, such as method for increasing pore size of the porous-low-k film and method for achieving an even distribution of the pores, has been tried.
However, when the porosity of the porous-low-k film is increased, mechanical strength of the insulating film is weakened. Thus, the insulating film is destroyed by stresses applied thereto in the processes of plasma, ashing, chemical-mechanical polishing (CMP) and the like. When the strength of the insulating film is weakened by the inclusion of many pores in the porous-low-k film, the insulating film may be peeled off from wiring adjacent thereto. Moreover, since the porous-low-k film has high hygroscopicity, the relative dielectric constant may change over time and it is difficult to control wiring capacity.